This invention relates to an image processing system for digital printer in conjunction with a scanner or document reader to serve as a copier.
Due to the popularity of office automation, it is common practice to equip an office or home with a scanner and a printer as shown in FIG. 1. (Note that the word xe2x80x9cscannerxe2x80x9d may also be termed as xe2x80x9cimage readerxe2x80x9d, xe2x80x9cimage inputting devicexe2x80x9d or xe2x80x9cdocument readerxe2x80x9d.) On the other hand, a digital copier is a bulky and expensive piece of equipment. It is desirable to reduce the number of equipment in an office or home to economize on space, expense and energy consumption.
A digital copier is actually a combination of a scanning device, a printing device and an image processor. As shown in FIG. 2, a digital copier consists of a scanning unit 101, a system control unit 102, an image processing unit 103, a printing unit 104 and an operation panel 105. Generally, the scanning unit 101 uses a charge coupled device (CCD) image sensor or contact image sensor (CIS) to scan the images of a document for each narrow region, i.e. on a pixel basis, to produce an analog image signal. The analog signal is quantized and converted into digital signals. After various kinds of signal processing in the image processing unit 103, the digital signal is applied to the printing unit 104 to reproduce the document images. The operation panel 105 is used to select various image processing methods and copy count.
The advantages of such a digital copier is having image manipulation capability and better printout quality compared with conventional low-end and mid-end copier. The drawback is its expense and bulkiness.
It can be seen that the function of a digital copier is redundant with that of a scanner and a printer. The processing and programming of a digital copier is similar to that of a scanner plus an image processing system and a printer.
At present, a printer is customarily used in connection with a personal computer. Data are transferred through an interface driver, such as the Centronics Interface. Due to the limitation of transmission speed and image processing of huge amount of data, it is not possible to increase the printing speed. Without any special image processing device, or real time image processing system or algorithm, the printer is incapable of achieving high quality and high speed printing.
According to a conventional method of binarized gradation processing an image by way of dither, the image signal read is directly compared as an analog signal with a dither threshold value or after it has been converted to the digital signal. This digital signal is compared with the dither threshold value and in this case, the dither threshold value is two-dimensionally changed in correspondence to the division of the read image. However, an image processed with the dither method results in poor resolution with saw-tooth edge in text and with Moire pattern.
The objects of this invention are to combine the functions of a scanner, a computer and a printer and to effect the following provisions:
1. A provision to store the scanned image input in the image processor, and to output directly the stored image rapidly to the printer;
2. A provision to translate the stored image and then to output the stored image rapidly to the printer;
3. A provision to output the stored image to a computer for storage;
4. A provision to translate the stored image and then to output the translated image to a computer;
5. A provision to output the scanned image input directly to a computer without image processing;
6. A provision to view the stored image in the computer and to output rapidly to the printer;
7. A provision to view or to edit the stored image, to view again after image processing, and then to output rapidly to the printer;
8. A provision to first transform the information in the computer into image, and then to output the information rapidly to the printer;
9. A provision to connect a video interface with a printer to fully utilize the high speed capability of the printer.
These objects are achieved by integrating the scanning function and the image processing function as an xe2x80x9cimage processing systemxe2x80x9d. The scanned image can be directly transmitted to a printing device for high quality reproduction serving a xe2x80x9cscan to printxe2x80x9d function. This invention can also transmit the scanned image with or without processing to a computer for further processing. The output from the computer is transformed into image information for rapid printout,